Copper-catalyzed silafunctionalization of alkynes using a silylboronic ester as a silicon source has recently progressed rapidly. Generally, the reaction affords a product with cis-stereoselectivity. We herein describe trans-selective 1,2-addition of silylboronic esters to internal arylalkynes, which was promoted efficiently by the CuOt-Bu/RCy₂P/NaOt-Bu catalysts. Moreover, we report a stereochemical switch to cis-addition in the reactions of Me₂(i-PrO)Si–B(pin) in hydrocarbon solvents including cyclohexane.